Late Devonian palaeobiogeography of marine organic-walled phytoplankton

Acritarchs and prasinophytes have generally been considered as organic-walled phytoplankton, and their distribution patterns play a significant role in palaeogeographical and palaeoclimatical reconstructions. In this paper the palaeobiogeography of Late Devonian phytoplankton (mainly Famennian) is quantitatively analyzed based on a global database consisting of 95 genera from 15 geographical units. The data are analyzed using cluster analysis, nonmetric multidimensional scaling, and minimum spanning tree analysis using the Jaccard, Ochiai, Kulczynski, and Yule's Y similarity coefficients. The results show that there was provincialism in the Late Devonian and three phytoplankton palaeobiogeographical realms could be identified: the West Gondwana, East Gondwana, and Boreal realms. There is a high degree of similarity between phytoplankton assemblages in East Gondwana (especially those in Australia and Iran) and Euramerica. Portugal (of the Iberian-Armorican block) was situated to the north of Algeria and probably acted as a stepping stone between Euramerica and West Gondwana. The closed oceanic surface circulation pattern in the Proto-Tethys Ocean between Euramerica and East Gondwana might have hindered the exchange of phytoplankton between East and West Gondwana. The phytoplankton province that had been typically confined to the higher latitudes was still present, while its characteristic genera gradually dispersed into the lower latitudes in the Late Devonian. There is a high similarity between phytoplankton assemblages from the western Junggar of Xinjiang, NW China and Euramerica. Latitude- and current-influenced palaeotemperature and oceanic circulation patterns are considered to have been the major determinants of the geographical distribution and evolution of marine phytoplankton in the Late Devonian.